Sion Jenkins has fought for nine years to clear his name, spending hundreds of hours in court and enduring three murder trials and two appeals.
From his arrest just weeks after the murder of his foster daughter Billie-Jo Jenkins in 1997 the former deputy head teacher always protested his innocence.
He appeared at a press conference to appeal for witnesses after the killing.
But a year later he was convicted of bludgeoning the 13-year-old to death at their home in Hastings, East Sussex.
A jury at Lewes Crown Court unanimously decided in 1998 he had battered Billie-Jo to death with a tent peg in a fit of rage as she painted patio doors at their Victorian semi-detached house.
English teacher Mr Jenkins and his social worker wife Lois, who had four daughters of their own, fostered Billie-Jo when she was nine years old.
She had been raised in east London, but moved with her foster family to Lower Park Road in Hastings, when Mr Jenkins became deputy head teacher of local boys' comprehensive, William Parker School.
He later secured the headship - a job he would have started in the September after Billie-Jo died.
Prosecutors claimed he was under pressure because he lied about his qualifications on the application form.
But head teacher at the time Roger Mitchell said he was an inspirational teacher.
"He was a highly intelligent teacher - very successful in the classroom," he said.
Billie-Jo was murdered at the house in Lower Park Road
"I never had any suspicions his qualifications were not appropriate for the way he presented himself, either with me or in the classroom with the children."
Mr Jenkins was a pillar of the community, a devout family man and committed Christian who stood as a Conservative candidate in local elections.
At the press conference after Billie-Jo's death, he said the family was totally devastated.
"We do not understand why my daughter has been murdered or what the motive could possibly be," he said.
"She had enormous ambitions and brought joy into the lives of everyone. "
Billie-Jo's friends at Helenswood School in Hastings paid tribute to the "friendly and popular" teenager.
One, Karen McEwan, said the school was in shock when she died.
"Everybody in tears and nobody knew what to say.
"It was not the same for weeks and weeks. It was such a traumatic thing to undergo."
In court, Mr Jenkins said he found Billie-Jo dead after returning from shopping with two of his daughters, Lottie and Annie.
He believed all along an intruder was responsible for the murder, saying Billie-Jo had complained on several occasions about a prowler.
Police arrested a 44-year-old man seen behaving strangely in the area, but he was later released.
Mr Jenkins was branded a "danger to the community" by the judge who sentenced him to life imprisonment in 1998 for murder.
Forensic evidence about blood found on Jenkins' clothes played a major part in his conviction.
Billie-Jo was beaten to death with a metal tent spike in 1997
The prosecution said microscopic blood spots on his fleece could only have happened when he was sprayed while carrying out the frenzied attack.
But fresh evidence at his second appeal backed the defence theory that the blood mist was caused as Jenkins went to Billie-Jo's aid as she took her last breaths.
Mr Jenkins served six years in prison before the first murder conviction was quashed.
Originally from Aberystwyth, Wales, he moved to Lymington, Hampshire with his second wife Christina after his release.
His formal acquittal comes at the end of a second retrial in which an Old Bailey jury could not reach a verdict.
Billie-Jo was buried in a City of London cemetery, near the home of her natural parents.